you might refer them to this section of the Oklahoma Credit code:
§14A-2-417. Surcharge for use of credit card.
No seller in any sales transaction may impose a surcharge on a cardholder who elects to use a credit card in lieu of payment by cash, check or similar means.
Added by Laws 1977, c. 135, § 2, emerg. eff. June 3, 1977.
I could not find any exemptions for municipal or state offices.
That may even supersede the restrictions that MC has placed as referred to earlier in the thread.
EDIT: I see Cust essentially pointed you guys in the direction of that statute, but I dug it out to see if I could find any exemptions.
Unless, of course, the state makes the claim this is not a "sales transaction", but rather a "fee collection" and that's how they are getting around the law.
I questioned this when I bought my truck tag back in the summer. They started to charge me a fee, and I said "hell no" and wrote them a check instead.